Contact structure

ABSTRACT

There is disclosed a contact structure for electrically connecting conducting lines formed on a first substrate of an electrooptical device such as a liquid crystal display with conducting lines formed on a second substrate via conducting spacers while assuring a uniform cell gap among different cells if the interlayer dielectric film thickness is nonuniform across the cell or among different cells. A first conducting film and a dielectric film are deposited on the first substrate. Openings are formed in the dielectric film. A second conducting film covers the dielectric film left and the openings. The conducting spacers electrically connect the second conducting film over the first substrate with a third conducting film on the second substrate. The cell gap depends only on the size of the spacers, which maintain the cell gap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a contact structure for electricallyconnecting together conducting lines formed on two opposite substrates,respectively, via conducting spacers and, more particularly, to acontact structure used in common contacts of an electrooptical devicesuch as a liquid crystal display.

2. Description of the Related Art

In recent years, liquid crystal displays have been extensively used inthe display portions of mobile intelligent terminals such as mobilecomputers and portable telephones including PHS (personal handyphonesystem) Also, active-matrix liquid crystal displays using TFTs asswitching elements are well known.

A liquid crystal display comprises two substrates and a liquid crystalmaterial sealed between them. Electrodes are formed on these twosubstrates to set up electric fields. A desired image or pattern isdisplayed by controlling the magnitudes of these electric fields. In theactive-matrix liquid crystal display, TFTs (thin-film transistors) areformed on one substrate to control the supply of voltage to each pixelelectrode. Therefore, this substrate is referred to as the TFTsubstrate. A counter electrode placed opposite to the pixel electrodesis formed on the other substrate and so it is referred to as the countersubstrate.

In the active matrix display, an electric field is produced between eachpixel electrode on the TFT substrate and the counter electrode on thecounter substrate, thus providing a display. The potential at each pixelelectrode on the TFT substrate is controlled by the TFT and thus isvaried. On the other hand, the counter electrode on the countersubstrate is clamped at a common potential. For this purpose, thecounter electrode is connected with an extractor terminal via a commoncontact formed on the TFT substrate. This extractor terminal isconnected with an external power supply. This connection structureclamps the counter electrode at the common potential.

The structure of the common contact of the prior art active-matrixliquid crystal display is next described briefly by referring to FIGS.12-14.

FIG. 12 is a top plan view of a TFT substrate 10. This TFT substratecomprises a substrate 11 having a pixel region is 12, a scanning linedriver circuit 13, and a signal line driver circuit 14. In the pixelregion 12, pixel electrodes and TFTs connected with the pixel electrodesare arranged in rows and columns. The scanning line driver circuit 13controls the timing at which each TFT is turned on and off. The signalline driver circuit 14 supplies image data to the pixel electrodes.Furthermore, there are extractor terminals 15 to supply electric powerand control signals from the outside. The substrate 11 makes connectionwith the counter electrode at common contact portions 16 a-16 d.

FIG. 13 is a cross-sectional view of the pixel region 12 and a commoncontact portion 16 representing the common contact portions 16 a-16 d. ATFT 17 and many other TFTs (not shown) are fabricated in the pixelregion 12 on the substrate 11. An interlayer dielectric film 18 isdeposited on the TFT 17. A pixel electrode 19 connected with the drainelectrode of the TFT 17 is formed on the interlayer dielectric film 18.

A precursor for the source and drain electrodes of the TFT 17 ispatterned into internal conducting lines 21 at the common contactportion 16. The interlayer dielectric film 18 is provided with arectangular opening. A conducting pad 22 is formed in this opening andconnected with the internal conducting lines 21. The pixel electrode 19and the conducting pad 22 are patterned from the same starting film.

FIG. 14 is a top plan view of the known common contact portion 16. Aregion located inside the conducting pad 22 and indicated by the brokenline corresponds to the opening formed in the interlayer dielectric film18.

As shown in FIG. 13, a counter electrode 24 consisting of a transparentconducting film is formed on the surface of a counter substrate 23. Thiscounter electrode 24 is opposite to the pixel electrodes 19 in the pixelregion 12 and to the conducting pad 22 at the common contact portion 16.

Spherical insulating spacers 25 are located in the pixel region 12 tomaintain the spacing between the substrates 11 and 23. A sphericalconducting spacer 26 is positioned at the common contact portion 16 andelectrically connects the counter electrode 24 with the conducting pad22. The pad 22 is electrically connected with the internal conductinglines 21, which in turn are electrically connected with an extractorterminal 15. This connection structure connects the counter electrode 24on the counter substrate 23 with the extractor terminal 15 on thesubstrate 11.

In the prior art liquid crystal display, the interlayer dielectric film18 is provided with the opening at the common contact portion 16, asshown in FIG. 13. Therefore, the cell gap G_(c) in the common contactportion is almost equal to the sum of the cell gap G_(p) in the pixelregion+the film thickness t of the interlayer dielectric film 18.

The cell gap G_(p) (also known as the cell spacing) in the pixel region12 is determined by the insulating spacers 25. It is common practice touse standardized spacers as the insulating spacers 25 and so if thespacers 25 have a uniform diameter, the cell gap G_(p) in the pixelregion 12 is substantially uniform among liquid-crystal cells. However,it is difficult to avoid nonuniformity of the cell gap G_(c) in thecommon contact portion among liquid-crystal cells.

The cell gap G_(c) in the common contact portion is constant since thecell gap G_(p) is constant because of the relation described above.Therefore, the cell gap G_(c) in the common contact portion depends onlyon the film thickness t of the interlayer dielectric film 18.Consequently, to make the cell gap G_(c) uniform among liquid-crystalcells, it is necessary that the film thickness t of this interlayerdielectric film 18 be uniform among cells. However, this is impossibleto circumvent.

Normally, the common contact portions of the liquid crystal display are2 to 4 in number. The film thickness t of the interlayer dielectric film18 may differ from location to location on the same substrate. In thiscase, the film thickness t may differ among different common contactseven on the same substrate.

Because of the aforementioned nonuniformity of the thickness t of theinterlayer dielectric film 18, the cell gap G_(c) in the common contactportion differs among different cells or different common contacts.Furthermore, the nonuniformity of the cell gap G_(c) results in the cellgap G_(p) in the pixel region to be nonuniform.

The cell gap G_(p) in the pixel region is affected more by thenonuniformity of the cell gap G_(c) in the common contact portion as thearea of the pixel region 12 becomes narrower than the area of the commoncontact portion. Especially, in the case of a projection display as usedin a projector, the problem of above-described nonuniformity of the cellgap G_(p) in the pixel region becomes conspicuous, because it is a quiteaccurate small-sized display of about 1 to 2 inches.

A standardized spacer is also used as the conducting spacer 26. Thediameter of this conducting spacer 26 is determined by the diameter ofthe insulating spacers 25 in the pixel region 12 and by the designthickness of the interlayer dielectric film 18. Where the thickness ofthe interlayer dielectric film 18 is much larger than the designedvalue, the cell gap G_(c) in the common contact portion becomes verylarge. This makes it impossible to connect the counter electrode withthe conducting pad well by the conducting spacer 26. In consequence, thecounter electrode cannot be clamped at the common potential. As aresult, a display cannot be provided.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a contact structurewhich is free of the foregoing problems, provides less nonuniform cellgap among different cells if the thickness of the interlayer dielectricfilm is nonuniform across the cell or among different cells, and reducespoor electrical contacts which would normally be caused by conductingspacers.

This object is achieved in accordance with the teachings of theinvention by a contact structure for connecting a conducting film formedon a first substrate with a conducting film formed on a second substrateopposite to the first substrate, the contact structure comprising: acell gap defined between the first and second substrates; a firstconducting film formed on the first substrate; a dielectric filmcovering the first conducting film; openings formed in the dielectricfilm to expose parts of the first conducting film by selectively leavingthe dielectric film; a second conducting film covering the dielectricfilm left and the openings; a third conducting film formed on the secondsubstrate; and conducting spacers held between the first and secondsubstrates and connecting the second and third conducting films. Thesecond conducting film is connected with the first conducting filmthrough the openings. The second conducting film, the conductingspacers, and the third conducting film are connected in turn on thedielectric film left. The conducting spacers maintain the cell gapbetween the first and second substrates.

One embodiment of the invention resides in a contact structure forconnecting a conducting film formed on a first substrate with aconducting film formed on a second substrate opposite to the firstsubstrate, the contact structure comprising: a cell gap defined betweenthe first and second substrates; a first conducting film formed on thefirst substrate; a dielectric film covering the first conducting film;openings formed in the dielectric film to expose parts of the firstconducting film; an insulator deposited on only portions of the firstconducting film exposed through the openings; a second conducting filmcovering the openings; a third conducting film formed on the secondsubstrate; and conducting spacers held between the first and secondsubstrates and connecting the second and third conducting films. Thesecond conducting film is connected with the first conducting filmthrough the openings extending through the insulator. The secondconducting film, the conducting spacers, and the third conducting filmare connected in turn through the openings extending through theinsulator. The conducting spacers maintain the cell gap between thefirst and second substrates.

Another embodiment of the invention resides in a contact structure forconnecting a conducting film formed on a first substrate of anelectrooptical device with a counter electrode formed on a secondsubstrate opposite to the first substrate, which has pixel electrodesformed thereover, the contact structure comprising: a cell gap definedbetween the first and second substrates; a first conducting film formedon the first substrate and under the pixel electrodes; an interlayerdielectric film covering the first conducting film; openings formed inthe interlayer dielectric film to expose parts of the first conductingfilm by selectively leaving the interlayer dielectric film; a secondconducting film defining the counter electrode formed on the secondsubstrate; a third conducting film covering the interlayer dielectricfilm left and the openings; and conducting spacers held between thefirst and second substrates and connecting the second and thirdconducting films. The second conducting film is connected with the firstconducting film through the openings. The third conducting film and thepixel electrodes are formed from a common starting film. The secondconducting film, the conducting spacers, and the third conducting filmare connected in turn on the dielectric film left. The conductingspacers maintain the spacing between the first and second substrates.

A further embodiment of the invention resides in a contact structure forconnecting a first conducting film formed over a first substrate of anelectrooptical device with a counter electrode formed on a secondsubstrate opposite to the first substrate, which has pixel electrodesformed thereon, the contact structure comprising: a cell gap definedbetween the first and second substrates; a first conducting film formedon the first substrate and under the pixel electrodes; an interlayerdielectric film covering the first conducting film; openings formed inthe interlayer dielectric film to expose parts of the first conductingfilm; an insulator formed on selected portions of the surface of thefirst conducting film extending through the openings; a secondconducting film covering the openings; a third conducting film definingthe counter electrode formed on the second substrate; conducting spacersheld between the first and second substrates and connecting the secondand third conducting films. The pixel electrodes and the secondconducting film are formed from a common starting film. The secondconducting film is connected with the first conducting film through theopenings extending through the insulator. The second conducting film,the conducting spacers, and the third conducting film are connected inturn on the insulator formed in the openings. The conducting spacersmaintain the cell gap between the first and second substrates.

A still other embodiment of the invention resides in a contact structurefor connecting a conducting film formed on a first substrate with aconducting film formed on a second substrate opposite to the firstsubstrate, the contact structure comprising: a cell gap defined betweenthe first and second substrates; a first conducting film formed on thefirst substrate; a dielectric film covering the first conducting film;openings formed in the dielectric film and exposing parts of the firstconducting film; a second conducting film covering the openings; a thirdconducting film formed over the second substrate; a fourth conductingfilm formed between the second substrate and the third conducting filmand in contact with the third conducting film; and conducting spacersheld between the first and second substrates. The first conducting film,the second conducting film, the conducting spacers, the third conductingfilm, and the fourth conducting films are connected in turn through theopenings. The spacers maintain the cell gap between the first and secondsubstrates.

Other objects and features of the invention will appear in the course ofthe description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of a common contact portionin accordance with the present invention;

FIGS. 2A and 2B are top plan views of the common contact portion shownin FIG. 1;

FIG. 3 is a top plan view of the TFT substrate of a liquid crystaldisplay in accordance with Example 1 of the invention;

FIG. 4 is a top plan view of the counter substrate of the liquid crystaldisplay in accordance with Example 1;

FIGS. 5A-5G are cross-sectional views illustrating a process sequencefor fabricating the TFT substrate shown in FIG. 3;

FIG. 6 is a fragmentary cross-sectional view of a pixel region and acommon contact portion of the liquid crystal display in accordance withExample 1;

FIG. 7 is a cross-sectional view similar to FIG. 6, but illustratingExample 2 of the invention;

FIG. 8 is a cross-sectional view similar to FIG. 6, but illustratingExample 3 of the invention;

FIG. 9 is an enlarged cross-sectional view of the common contact portionshown in FIG. 7;

FIG. 10 is an enlarged cross-sectional view of the common contactportion shown in FIG. 8;

FIG. 11 is a top plan view of the common contact portion shown in FIG.8;

FIG. 12 is a top plan view of the TFT substrate of the prior art liquidcrystal display;

FIG. 13 is a cross-sectional view of a pixel region and a common contactportion on the TFT substrate shown in FIG. 12; and

FIG. 14 is a top plan view of the common contact portion shown in FIG.13.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

The present embodiment of this invention is described by referring toFIGS. 1, 2A and 2B. FIG. 1 is a fragmentary cross-sectional view of acommon contact portion of a liquid crystal display in accordance withthe present embodiment. FIGS. 2A and 2B are top plan views of the TFTsubstrate of the liquid crystal display. The structure of a region 120shown in FIG. 2A is depicted in the enlarged cross section of FIG. 1.

As shown in FIG. 13, in the prior art structure, the spacers in thepixel region 12 are located over the interlayer insulating film 18 viathe pixel electrode 19. However, the interlayer dielectric film 18 doesnot exist under the conducting pad 22 at the common contact portion 16.Hence, the cell gap G_(c) in the common contact portion depends on thethickness of the interlayer dielectric film 18.

Accordingly, in the present embodiment, an insulator, or a dielectric,is inserted under the conducting pad in the common contact portion.Conducting spacers are placed on top of the dielectric, so that the cellgap G_(c) in the contact portion does not depend on the thickness of theinterlayer dielectric film 18. In the present embodiment, openings areformed, selectively leaving the interlayer dielectric film 18.

In the present embodiment, as shown in FIG. 1, a first conducting film103 is formed on a first substrate 101. A dielectric film 104 isdeposited on the first conducting film 103. The dielectric film 104 isselectively left to form openings 111 that expose parts of the firstconducting film 103. A second conducting film 105 is formed so as tocover the left parts of the dielectric film, 104 a, and the openings111.

A third conducting film 106 is formed on the second substrate 102.Conducting spacers 107 are sandwiched between the first substrate 101and the second substrate 102.

In the prior art opening 110 shown in FIG. 2A, the dielectric film 104has been fully removed. In the present embodiment, the dielectric film104 is selectively left to form the dielectric film portions 104 a andthe openings 111. The openings 111 expose parts of the first conductingfilm 103. The first conducting film 103 is connected with the secondconducting film 105 at these openings 111.

On the first substrate 101, the left dielectric film 104 a is closest tothe second substrate 102; therefore, on the left dielectric film 104 a,the second conducting film 105 formed on the first substrateelectrically connects with the third conducting film 106 formed on thesecond conducting film 102 through the conducting spacer 107, as shownin FIG. 1.

In region 110, the left dielectric film 104 a is closest to the secondsubstrate; therefore, the conducting spacers 107 electrically connectingthe second conducting film 105 with the third conducting film 106maintain the gap G between the substrates. Consequently, this gap G isdependent only on the size of the conducting spacers 107. Therefore,where the conducting spacers 107 are uniform among liquid-crystal cells,the gap G can be made uniform among cells, even if the thickness t ofthe dielectric film 104 differs among cells.

In the present embodiment, it is desired that the area of each opening111 be sufficiently larger than the area occupied by each conductingspacer and offer space so that the conducting spacers can move freely,because the spacers 107 existing in the openings 111 do not contributetoward maintaining the gap. Otherwise, plural conducting spacers 107would be stacked on top of each other, making it impossible to maintainthe cell gap G uniform across the cell.

Also in the present embodiment, it is desirable that the area of thesurface of each left dielectric film portion 104 a be sufficientlylarger than the area occupied by each conducting spacer 107, assuringarrangement of the conducting spacers 107 if the spacers 107 are notpositioned over the dielectric film 104 a with certainty, it will not bepossible to make electrical connections between the first and secondsubstrates. Furthermore, the gap will not be maintained.

The openings 111 are formed as shown in FIG. 2A in the presentembodiment. The relation between the left dielectric film 104 a and eachopening 111 may be reversed as shown in FIG. 2B. It is that noted FIG. 1is an enlarged view of the region 120 indicated by the broken line inFIG. 2B.

Embodiment 2

The present embodiment is described by referring to FIGS. 1 and 2A. FIG.1 is a cross-sectional view of a common contact portion of the liquidcrystal display in accordance with the present embodiment. FIG. 2A is atop plan view of the TFT substrate of the liquid crystal display. FIG. 1is an enlarged cross-sectional view of the region 120 indicated by thebroken line in FIG. 2A.

A dielectric is inserted under a conducting pad in the common contactportion, in the same manner as in Embodiment 1. Conducting spacers arepositioned on the dielectric. Thus, the cell gap G_(c) in the commoncontact portion does not depend on the thickness of the interlayerdielectric film 18. The present embodiment is characterized in that thedielectric film 18 is selectively left to form openings.

In particular, in the present embodiment, the dielectric layer is formedunderneath the conducting pad 22. The conducting spacers are positionedon the dielectric. Consequently, the cell gap G_(c) in the commoncontact portion is not dependent on the thickness of the interlayerdielectric film 18.

Referring to FIG. 1, a first conducting film 103 is formed on top of afirst substrate 101. A dielectric film 104 covers the first conductingfilm 103. The dielectric film 104 is provided with openings 111 toselectively expose the surface of the first conducting film 103. Theexposed portions of the dielectric 104 are indicated by 104 a. A secondconducting film 105 is formed to cover the openings 111.

A third conducting film 106 is formed on the second substrate 102.Conducting spacers 107 are located between the first substrate 101 andthe second substrate 102.

FIG. 2A is a top plan view of the TFT substrate, and in which the secondconducting film 105 is not yet deposited. In FIG. 2A, the region 110indicated by the broken line corresponds to the opening for the commoncontact formed in the interlayer dielectric film 18 of the prior artstructure. A dielectric 104 a is selectively deposited to leave portionsof the first conducting film 103 to be exposed.

The first conducting film 103 is exposed at locations where thedielectric 104 a is not deposited. The exposed portions of the firstconducting film 103 are connected with the overlying second conductingfilm 105.

On the first substrate 101, the dielectric 104 a is closest to thesecond substrate. As shown in FIG. 1, on the dielectric 104 a,conducting spacers 107 electrically connect the second conducting film105 on the first substrate 101 with the third conducting film 106 on thesecond substrate 102.

The dielectric 104 a is closest to the second substrate 102. Therefore,the conducting spacers 107 electrically connecting the second conductingfilm 105 with the third conducting film 106 hold the cell gap G. Inconsequence, the gap G is dependent only on the size of the conductingspacers 107. Where the spacers 107 are uniform in size, the cell gap Gcan be rendered uniform among liquid-crystal cells even if the thicknesst of the dielectric film 104 differs among cells.

In the present embodiment, the area of each portion not covered with thedielectric 104 a is preferably sufficiently wider than the area occupiedby one conducting spacer 107 and permits the conducting spacers 107 tomove freely, because the spacers 107 existing in the regions where thedielectric 104 a is not present do not contribute toward maintaining thegap. Otherwise, plural conducting spacers 107 would be stacked on top ofeach other, making it impossible to maintain the cell gap G uniformacross the cell.

Also in the present embodiment, it is desirable that the area of eachportion of the dielectric film 104 a be sufficiently larger than thearea occupied by one conducting spacer 107 and that the conductingspacers 107 be arranged with certainty. If the spacers 107 are notpositioned on the dielectric film 104 a with certainty, it will not bepossible to make electrical connections between the first and secondsubstrates. Furthermore, the cell spacing will not be maintained.

In this embodiment, the dielectric 104 a is deposited as shown in FIG.2A. The relation between the regions where the dielectric 104 a isdeposited and each region where the first conducting film 103 is exposedmay be reversed as shown in FIG. 2B.

EXAMPLE 1

In this example, the present invention is applied to a common contactportion of a reflection-type liquid crystal display. FIG. 3 is a topplan view of the TFT substrate of this liquid crystal display. FIG. 4 isa top plan view of the counter substrate of the liquid crystal display.

Referring to FIG. 3, the TFT substrate 200 comprises a substrate 201having a pixel region 202, a scanning line driver circuit 203, and asignal line driver circuit 204. Pixel electrodes and TFTs connected withthe pixel electrodes are arranged in rows and columns in the pixelregion 202. The scanning line driver circuit 203 controls the timing atwhich each TFT is turned on and off. The signal line driver circuit 204supplies image data to the pixel electrodes. Extractor terminals 205 arealso provided to supply electric power and control signals from theoutside. Common contact portions 206 a-206 d form junctions with thecounter electrode.

As shown in FIG. 4, the counter substrate 250 comprises a substrate onwhich a counter electrode 252 consisting of a transparent conductingfilm is deposited. A central rectangular region 253 is opposite to thepixel region 202 of the TFT substrate 200. Four corner regions 254 a-254d are electrically connected with the contact portions 206 a-206 d,respectively, of the TFT substrate 200.

As shown in FIG. 3, conducting pads are formed in the common contactportions 206 a-206 d, respectively, of the TFT substrate 200. Theseconducting pads are electrically connected together by internalconducting lines 207 a-207 c. The internal lines 207 a and 207 b extendto the extractor terminals 205 and are electrically connected withcommon terminals 205 a and 205 b, respectively.

A process sequence for manufacturing the pixel region 202 and the commoncontact portion 206 a-206 d on the TFT substrate is next described byreferring to FIGS. 5A-5G.

First, the substrate 201 having an insulating surface was prepared. Inthe present example, a silicon oxide film was formed as a buffer film onthe glass substrate. An active layer 302 consisting of a crystallinesilicon film was formed over the substrate 201. Although only one TFT isshown, millions of TFTs are built in the pixel region 202 in practice.

In the present example, an amorphous silicon film was thermallycrystallized to obtain the crystalline silicon film. This crystallinesilicon film was patterned by an ordinary photolithographic step toobtain the active layer 302. In this example, a catalytic element suchas nickel for promoting the crystallization was added during thecrystallization. This technology is described in detail in JapaneseUnexamined Patent Publication No. 7-130652.

Then, a silicon oxide film 303 having a thickness of 150 nm was formed.An aluminum film (not shown) containing 0.2% by weight of scandium wasdeposited on the silicon oxide film 303. The aluminum film waspatterned, using a resist mask 304, into an island pattern 305 fromwhich gate electrodes will be formed (FIG. 5A).

The present example made use of the anodization technique described inJapanese Unexamined Patent Publication No. 7-135318. For furtherinformation, refer to this publication.

First, the island pattern 305 was anodized within a 3% aqueous solutionof oxalic acid while leaving the resist mask 304 on the island pattern305, the mask 304 having been used for the patterning step. At thistime, an electrical current of 2 to 3 mV was passed, using a platinumelectrode as a cathode. The voltage was increased up to 8 V. Since theresist mask 304 was left on the top surface, porous anodic oxide film306 was formed on the side surfaces of the island pattern 305 (FIG. 5B).

After removing the resist mask 304, anodization was carried out within asolution prepared by neutralizing a 3% aqueous solution of tartaric acidwith aqueous ammonia. At this time, the electrical current was set to5-6 mV. The voltage was increased up to 100 V. In this way, a denseanodic oxide film 307 was formed.

The above-described anodic oxidation step defined the unoxidized islandpattern 305 into gate electrodes 308. Internal connecting lines 207 cinterconnecting the common contact portions 206 c and 206 d were createdfrom the aluminum film described above simultaneously with the gateelectrodes 308.

Then, using the gate electrodes 308 and surrounding anodic oxide film306, 307 as a mask, the silicon oxide film 303 was etched into a gateinsulating film 309. This etching step relied on dry etching using CF₄gas (FIG. 5C).

After the formation of the gate insulating film 309, the porous anodicoxide film 307 was removed by wet etching using Al mixed acid.

Thereafter, impurity ions for imparting one conductivity type wereimplanted by ion implantation or plasma doping. Where N-type TFTs areplaced in the pixel region, P (phosphorus) ions may be implanted. WhereP-type TFTs are placed, B (boron) ions may be implanted.

In the present example, the above-described process for implanting theimpurity ions was carried out twice by ion implantation. The first stepwas performed under a high accelerating voltage of 80 keV. The systemwas so adjusted that the peak of the impurity ions was brought under theends (protruding portions) of the gate insulating film 309. The secondstep was effected under a low accelerating voltage of 5 keV. Theaccelerating voltage was adjusted so that the impurity ions were notimplanted under the ends (protruding portions) of the gate insulatingfilm 309.

In this way, a source region 310, a drain region 311, lightly dopedregions 312, 313, and a channel region 314 for the TFT were formed. Thelightly doped region 313 on the side of the drain region 311 is alsoreferred to as the LDD region (FIG. 5D).

At this time, it is preferable to implant the impurity ions to such adosage that the source and drain regions 310 and 311, respectively,exhibit a sheet resistance of 300 to 500 Ω/□. In addition, it isnecessary to optimize the lightly doped regions 312 and 313 according tothe performance of the TFT. After the impurity ion implantation step, athermal treatment was carried out to activate the impurity ions.

Then, a 1 μm-thick-silicon oxide film was formed as a first interlayerdielectric film 315. The thickness of the interlayer dielectric film 315was set to 1 μm to flatten the surface of the first interlayerdielectric film 315 as much as possible. This could mitigate theprotrusions due to the gate electrodes 308.

The first interlayer dielectric film 315 may be made of silicon nitrideor silicon oxynitride, as well as silicon oxide. Alternatively, thefirst interlayer dielectric film 315 may be a multilayer film of thesematerials.

Contact holes for gaining access to the source and drain regions 310 and311, respectively, were created in the first interlayer dielectric film315. Contact holes for allowing access to the internal-conducting lines207 c were formed in the common contact portions 206 c and 206 d. Then,a conducting film forming a precursor for source and drain electrodes316 and 317, respectively, and for internal conducting lines 318 wasdeposited.

In this example, the conducting film was created from a multilayer filmof titanium (Ti), aluminum (Al), and titanium (Ti) by sputtering. Eachof the titanium layers was 100 nm thick, while the aluminum layer was300 nm thick. This multilayer film was patterned to form a sourceelectrode 316, a drain electrode 317, and internal conducting lines 318(FIG. 5E).

The internal conducting lines 318 shown FIG. 5E correspond to theinternal conducting lines 207 a and 207 b shown in FIG. 3. Theseconducting lines 207 a and 207 b were connected with internal conductinglines 207 c at the common contact portions 206 c and 206 d. The internalconducting lines 207 c and the gate electrode 308 were created by thesame processing steps.

Subsequently, an organic resinous film was formed as a second interlayerdielectric film 319 to a thickness of 1 to 2 μm. Polyimide, polyamide,polyimidamide, acrylic resin, or other material may be used as thematerial of the organic resinous film. The organic resinous materialacts to planarize the surface of the second interlayer dielectric film319. This is important to make the cell gap uniform. In the presentexample, polyimide was deposited as the second interlayer dielectricfilm 319 to a thickness of 1 μm.

Then, contact holes 320 and 321 were formed in the second interlayerdielectric film 319 to have access to the drain electrode 317 and to theinternal conducting lines 318, respectively. The contact holes 321 forthe internal conducting lines 318 were formed in the openings 111 shownin FIG. 2A. That is, rectangular holes measuring 100 μm×100 μm werearranged in 5 rows and 5 columns within the rectangular region 110measuring 1.1 mm×1.1 mm. These holes were spaced 100 μm from each other.Moreover, contact holes for connecting the internal conducting lines 318(207 a and 207 b) with the common terminals 205 a and 205 b at theextractor terminals 205 were formed.

As described later, the size of each hole was set to 100 μm×100 μm toset the diameter of the conducting spacers to 3.5 μm in this example.This provides sufficient space so that the conductive spacer located atthis position can move. Hence, the conducting spacers are prevented frombeing stacked on top of each other.

The area of the left portions of the interlayer dielectric film 319 inthe common contact portions is large enough to permit the conductingspacers to move. This assures that the conducting spacers are arrangedin these regions. Consequently, the conducting spacers positioned inthese regions can maintain the cell gap and make electrical connectionsreliably.

A thin metal film which would later be made into pixel electrodes 322and a conducting pad 323 were formed to a thickness of 100 to 400 nm. Inthe present example, the thin metal film was made of an aluminum filmcontaining 1 wt % titanium and deposited to a thickness of 300 nm bysputtering. Then, the thin metal film was patterned to form the pixelelectrodes 322 and the conducting pad 323. This pad 323 measured 1.1mm×1.1 mm, was rectangular, and covered the contact holes 321. Theextractor terminals 205 were also patterned. Thus, the TFT substrate wascompleted (FIG. 5G).

Referring to FIG. 6, the counter substrate 250 comprised a transparentplate 251 on which the counter electrode 252 was formed from an ITOfilm. A glass or quartz substrate can be used as the substrate 251.

Then, the TFT substrate 200 and the counter substrate 250 were bondedtogether. This bonding step may be a well-known cell assembly method.

First, a sealing material was applied to one of the TFT substrate 200and the counter substrate 250. In this example, the sealing material wasapplied to the counter substrate 250. A UV-curable and thermosettingresin was used as the sealing material. This sealing material wasapplied around the substrate along straight lines except for the liquidcrystal injection port by a sealant dispenser. A sealing material towhich 3.0 wt % spherical conducting spacers 401 were added was appliedto regions 254 a-254 d shown in FIG. 4. The sealing material to whichthe conducting spacers were added functioned as an anisotropicconducting film.

Generally, the conducting spacers 401 consist of resinous spheres coatedwith a conducting film. In the present example, the conducting spacers401 were coated with gold (Au). The diameter of the conducting spacers401 may be larger than the cell gap by about 0.2 to 1 μm. In thisexample, the conducting spacers 401 had a diameter of 3.5 μm to set thecell gap to 3 μm. After applying the sealing material, it wastemporarily baked.

Thereafter, spacers 402 were dispersed onto one of the TFT substrate 200and the counter substrate 250 to maintain the cell gap. In this example,the spacers 402 were applied to the counter substrate 250. To set thecell gap to 3 μm, spherical spacers of a polymeric material were used asthe spacers 402.

Then, the TFT substrate 200 and the counter substrate 250 were heldopposite to each other, and they were pressed against each other untilthe cell gap in the pixel region was decreased to the diameter of thespacers 402. Under the pressed state, UV light was directed at thisassembly for more than 10 seconds to cure the sealing material. The cellgap was fixed. Then, the assembly was heated under pressure, thusenhancing the adhesive strength.

Subsequently, a liquid crystal material was injected, and the entrancehole was sealed off, thus completing the cell assembly process. As shownin FIG. 6, the counter electrode 252 on the counter substrate 250 waselectrically connected with the conducting pad 323 on the TFT substrate200 by the conducting spacer 401. On the TFT substrate, the conductingpad 323 connected the internal conducting lines 318 with the commonterminals. This connection structure permitted the counter electrode 252on the counter substrate 250 to be connected with an external powersupply via the conducting lines on the TFT substrate. FIG. 1 is anenlarged view of the common contact portion of FIG. 6.

In the present example, to set the cell gap to 3 μm, the spacers 402applied to the pixel region had a diameter of 3 μm. The diameter of theconducting spacers 401 was 3.5 μm. Setting the diameter of theconducting spacers greater than the diameter of the spacers 402 (i.e.,the cell gap) made reliable the connection between the counter electrode252 and the conducting pad 318. When the two plates were being clampedtogether to bond them together, the conducting spacers 401 were crushedbecause they were larger in diameter than the cell gap. This increasedthe areas of the portions in contact with the counter electrode 252 andwith the conducting pad 318, respectively. Hence, the electricalconnection was rendered more reliable. Furthermore, the cell gap couldbe maintained at the same dimension as in the pixel region.

In this example, the internal conducting lines 318 were made of theprecursor for the source and drain electrodes 316 and 317, respectively.It is only necessary for the internal conducting lines 318 to be underthe pixel electrodes 322. For instance, where a black matrix consistingof a conducting film of titanium or the like is formed inside the secondinterlayer dielectric film 315, the internal conducting lines 318 can beformed from this conducting film.

In the present example, it is important to flatten the surface of thesecond interlayer dielectric film 319 on which the pixel electrodes 322are formed in order to make uniform the cell gap. Also, the flatness ofthe surface of the first interlayer dielectric film 315 where theinternal conducting lines 318 are formed is important.

Methods of obtaining an interlayer dielectric film having a flat surfaceinclude a method of increasing the thickness of the interlayerdielectric film, a leveling method using an organic resinous film, amechanical polishing method; and etch-back techniques. The presentexample made use of the method of increasing the film thickness toplanarize the first interlayer dielectric film 315. Also, the method ofrelying on leveling using an organic resinous film was used to flattenthe first interlayer dielectric film 315. Other methods may also beemployed for the same purpose.

In a liquid crystal display in accordance with the present example, adichroic dye may be dispersed in the liquid crystal layer. Orientationfilms may be deposited on the TFT substrate and on the countersubstrate. Color filters may be formed on the counter substrate. Thepractitioner may appropriately determine the kind of the liquid crystallayer, the presence or absence of the orientation films and the colorfilters according to the driving method, the kind of the liquid crystal,and other factors.

For instance, where the color filters are mounted on the countersubstrate 250, the color filters are not formed at the common contactportions and so steps are formed between the pixel region and the commoncontact portions on the counter substrate. To compensate for thesesteps, it is necessary to make the diameter of the conducting spacerslarger by an amount almost equal to the thickness of the color filter.

In the present example, the liquid crystal display is of the reflectiontype. A transmissive liquid crystal display may also be fabricated. Inthis case, the precursor for the pixel electrode and for the conductingpad may be made of a transparent ITO film or the like.

In the example described above, the transistor is a coplanar TFT that isa typical top-gate TFT. It may also be a bottom-gate TFT. In addition,thin-film diodes, metal-insulator-metal (MIM) devices, metal-oxidevaristors, and other devices can be used, as well as the TFTs.

EXAMPLE 2

The present example is a modification of the common contact portions ofExample 1. FIG. 7 is a fragmentary cross-sectional view of anactive-matrix display in accordance with the present example. Theconfiguration of a TFT substrate shown in FIG. 7 is the same as theconfiguration shown in FIG. 6, and some reference numerals are omitted.Like components are indicated by like reference numerals in both FIGS. 6and 7. FIG. 9 is an enlarged view of the common contact portion shown inFIG. 7.

In Example 1 shown in FIG. 6, the counter electrode 252 consists of anITO film that is a transparent conducting film. Therefore, the counterelectrode 252 and the conducting spacers 401 are larger in electricalresistance than metal films. The present example is intended to reducethis electrical resistance.

Accordingly, the resistance value between the counter electrode 252 andthe conducting spacers 401 can be lowered by forming a metallizationlayer on the counter substrate 250 and patterning the metallizationlayer into conducting pads, or conducting film, 501 at the commoncontact portions 254 a-254 d. Importantly, the conducting film formingthe conducting pads 501 is lower in electrical resistance than theconducting film forming the counter electrode 252.

Where the black matrix on the counter substrate is formed from aconducting film as consisting of chromium, the connecting pads 501 canbe formed from this conducting film. When the conducting film ispatterned to form the black matrix, the connecting pad 501 may becreated.

EXAMPLE 3

The present example is a modification of Example 2. FIG. 8 is afragmentary cross-sectional view of an active-matrix display inaccordance with the present example. The TFT substrate shown in FIG. 8is identical in structure with that shown in FIG. 6, and some referencenumerals are omitted in FIG. 8. It is noted like components are denotedby like reference numerals in both FIGS. 6 and 8. FIG. 10 is an enlargedview of the common contact portion of FIG. 8.

In Example 1, both counter substrate 251 and counter electrode 252 aretransparent to light and so the distribution of the conducting spacers401 on the common contact portions can be visually observed from theside of the counter substrate 250 after both substrates have been bondedtogether. In Example 2, however, the connecting pad 501 consisting ofmetallization layer is formed and, therefore, the distribution of theconducting spacers 401 cannot be visually checked.

The present example is intended to permit one to visually observe thedistribution of the conducting spacers 401 while a connecting pad isprovided to lower the resistance value. For this purpose, the connectingpad, 601, is provided with openings formed at selected locations. Onecan observe the conducting spacers 401 through these openings.

FIG. 11 is a top plan view of the contact portions according to thepresent example, taken from the side of the counter substrate. FIG. 10is a cross-sectional view of the common contact portion in a region 600surrounded by the broken line. As shown in FIG. 11, the conducting pad601 is formed with openings 602. In each opening 602, there exist onlythe counter substrate 251 and the counter electrode 252, both of whichhave transparency. Hence, the distribution of the conducting spacers 401can be observed through the openings 602.

To maintain the cell gap, the openings 602 should be formed opposite tothe contact holes 321 formed in the second interlayer dielectric film ofthe TFT substrate. At these locations, the conducting spacers 401 arenot in contact with the counter electrode. The area of each opening 602should be slightly larger than the area of each contact holes 321 formedin the second interlayer dielectric film, i.e., about several to thirtypercent greater. The number of the openings 602, their arrangement, andtheir shape are not limited to the example of FIG. 11. Rather, one canarbitrarily set these geometrical factors.

Setting each opening 602 in the connecting pad 601 slightly larger thaneach contact holes 321 makes it possible to visually check theconducting pad 602 on the second interlayer dielectric film 319, whichcontributes to electrical connection.

In Examples 2 and 3, the cell gap in the common contact portions is madeuniform. At the same time, the contact resistances of the conductingspacers 401 and of the counter electrode 252 are decreased. If the mainpurpose is to lower these resistance values, the common contact portionson the TFT substrate may have the prior art structure as shown in FIG.13. In this case, any of the connecting pads 501 and 601 described inExamples 2 and 3, respectively, may be formed between the substrate 23and the counter electrode 24 at the common contact portions 16 shown inFIG. 13.

In Examples 1-3 described above, the present invention is applied toactive-matrix liquid crystal displays. The contact structure inaccordance with the present invention is applicable to any apparatushaving a contact structure for electrically connecting conductors formedon one substrate with conducting conductors formed on the other oppositesubstrate via conducting spacers. For example, the novel contactstructure can connect ICs built on different silicon wafers.

The common contact structure in accordance with the present inventioncan eliminate variations of the cell gap among liquid-crystal cells evenif the film thickness varies among interlayer dielectric films. Also,poor contacts due to conducting spacers can be reduced.

In particular, in accordance with the present invention, the cell gapdepends only on the size of conducting spacers. Therefore, where theconducting spacers are uniform in size, the cell gap between oppositesubstrates or plates can be made uniform among different liquid-crystalcells, if the thickness of a dielectric film electrically insulating thefirst and second conducting films is different among differentliquid-crystal cells.

1. An active matrix display device comprising: a display region formedover a substrate; a plurality of extractor terminals formed over thesubstrate; and a counter electrode covering the display region, whereinthe extractor terminals are commonly and electrically connected to thecounter electrode.
 2. An active matrix display device comprising: adisplay region formed over a substrate; a plurality of extractorterminals formed over the substrate; at least one common contact regionformed adjacent to the display region; and a counter electrode coveringthe display region, wherein the extractor terminals are commonly andelectrically connected to the counter electrode via the common contactregion.
 3. An active matrix display device comprising: a display regionformed over a substrate; a plurality of extractor terminals formed overthe substrate; a counter electrode covering the display region; and atleast one common contact region formed adjacent to the display regionand electrically connected to the extractor terminals via an internalconducting line, wherein the extractor terminals are commonly andelectrically connected to the counter electrode via the common contactregion, wherein the internal conducting line extends along at leastthree sides of the display region.
 4. An active matrix display devicecomprising: a display region formed over a substrate; a plurality ofextractor terminals formed over the substrate; a counter electrodecovering the display region; at least one common contact region formedadjacent to the display region and electrically connected to theextractor terminals via an internal conducting line; and a displaymedium formed between the display region and the counter electrode,wherein the extractor terminals are commonly and electrically connectedto the counter electrode via the common contact region, wherein theinternal conducting line extends along at least three sides of thedisplay region.
 5. An active matrix display device comprising: a pixelregion and a driver circuit formed over a substrate; a plurality ofextractor terminals formed over the substrate; and a counter electrodecovering at least the pixel region, at least one common contact regionformed adjacent to the pixel region and electrically connected to theextractor terminals via an internal conducting line, wherein theextractor terminals are commonly and electrically connected to thecounter electrode via the common contact region, wherein the internalconducting line extends along at least three sides of the pixel region.6. An active matrix display device comprising: a display region formedover a substrate; a plurality of extractor terminals formed over thesubstrate; a counter electrode covering the display region; and at leastone common contact region formed adjacent to the display region andelectrically connected to the extractor terminals via an internalconducting line, wherein the extractor terminals are commonly andelectrically connected to the counter electrode via the common contactregion, wherein the internal conducting line extends along a side edgeof the substrate which is opposed to the extractor terminals.
 7. Anactive matrix display device comprising: a display region formed over asubstrate; a plurality of extractor terminals formed over the substrate;a counter electrode covering the display region; at least one commoncontact region formed adjacent to the display region and electricallyconnected to the extractor terminals via an internal conducting line;and a display medium formed between the display region and the counterelectrode, wherein the extractor terminals are commonly and electricallyconnected to the counter electrode via the common contact region,wherein the internal conducting line extends along a side edge of thesubstrate which is opposed to the extractor terminals.
 8. An activematrix display device comprising: a pixel region and a driver circuitformed over a substrate; a plurality of extractor terminals formed overthe substrate; and a counter electrode covering at least the pixelregion, at least one common contact region formed adjacent to the pixelregion and electrically connected to the extractor terminals via aninternal conducting line, wherein the extractor terminals are commonlyand electrically connected to the counter electrode via the commoncontact region, wherein the internal conducting line extends along aside edge of the substrate which is opposed to the extractor terminals.